Comet
A comet is a small Solar System body composed mainly of ice, dust, and organic compounds. As they approach the Sun, cometary ices sublimate, releasing gas and dust that form the glowing coma and distinctive tails—often extending millions of kilometers.
Comets originate from two primary reservoirs: the Kuiper Belt—home to short-period comets with orbits under ~200 years—and the distant Oort Cloud, which sends long-period comets with orbits spanning thousands of years. Occasionally, interstellar objects like ‘Oumuamua pass through our system, appearing comet-like.
They are “dirty snowballs” and among the most primitive remnants of the early Solar System, preserving original ices and organic material from 4.6 billion years ago.
Landmark missions include ESA’s Rosetta—with its lander Philae—which orbited and sampled Comet 67P/Churyumov–Gerasimenko (2014–2016). NASA’s Deep Impact struck Comet Tempel 1 in 2005 to analyze interior composition.
These missions discovered complex organic molecules, including amino-acid precursors, and supported the theory that comets may have delivered water and prebiotic compounds to early Earth.
Looking ahead, ESA–JAXA’s Comet Interceptor (launch planned for 2029) intends to perform a rapid flyby of a dynamically new or interstellar comet, using multiple spacecraft to sample both nucleus and coma environments.
Comets are studied across the electromagnetic spectrum—from radio to gamma rays—using telescopes and spacecraft to understand composition, internal structure, activity, and their roles in planetary formation, the evolution of the solar system, and the origin of life.
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APODs including "Comet"
Comet Tsuchinshan-ATLAS Flys Away
19 October 2024
These six panels follow daily apparitions of comet C/2023 A3 Tsuchinshan-ATLAS as it moved away from our fair planet during the past week. The images were taken with the same camera and lens at the indicated dates and locations from California, planet Earth. At far right on October 12 the visitor from the distant Oort cloud was near its closest approach, some 70 million kilometers (about 4 light-minutes) away. Its bright coma and long dust tail were close on the sky to the setting Sun but still easy to spot against a bright western horizon. Over the following days, the outbound comet steadily climbs above the ecliptic and north into the darker western evening sky, but begins to fade from view. Crossing the Earth's orbital plane around October 14, Tsuchinshan-ATLAS exhibits a noticeable antitail extended toward the western horizon. Higher in the evening sky at sunset by October 17 (far left) the comet has faded and reached a distance of around 77 million kilometers from planet Earth. Hopefully you enjoyed some of Tsuchinshan-ATLAS's bid to become the best comet of 2024. This comet's initial orbital period estimates were a mere 80,000 years, but in fact it may never return to the inner Solar System. Growing Gallery: Comet Tsuchinshan-ATLAS in 2024